(A) Field of the Invention
The present invention relates to display panel technologies, and more specifically, to a backlight unit.
(B) Description of the Related Art
The recent trend to use light emitting diodes (LEDs) as light sources for notebook computers provides advantages such as thin profile and low power consumption. However, LEDs are a point light source, and create a light pattern that follows a Lambertian distribution. After light enters a light guide plate, according to Snell's law the light will be more concentrated. Therefore, a mixed light region with a certain length is needed to expand the light into a uniform plane light source. For example, the back of the light guide plate may be provided with tiny protrusions, and varying the protrusion distribution can decrease or increase total reflection damage so as to obtain a uniform plane light source.
In consideration of power saving and light weight requirements, the decrease of the number of LEDs serving as light sources and the decrease of the mixed region between the panel and display region have to be achieved concurrently. As a result, the LED hot spot mura problem, which results in interlaced bright-and-dark picture on LED light entry side, cannot be completely resolved by the tiny protrusions on the back of the light guide plate.
A method for improvement is to add a row of microstructures at a side near the LED light entry side, as shown in FIG. 1. The light guide plate 11 is further provided with a microstructure 12 at the light entry side of LEDs 13, and the dashed line area is a picture display area 14. However, the microstructure 12 may have a disadvantage, i.e., the angle between a part of light refracted by the microstructure 12 and the Y-axis may be too large. Because the light guide plate 11 of the backlight unit 10 may be supported by a white frame 15, the light with a large angle after being transmitted through the light guide plate 11 will be emitted from the sides and reflected to the light guide plate 11 by the frame 15. This is called picture light leakage.
Therefore, there is a need to make the display panel thin and simultaneously avoid the problems of LED hot spot mura and side light leakage.